Etching apparatus

ABSTRACT

When a substrate is etched by using a processing gas including a first gas containing halogen and carbon and having a carbon number of two or less per molecule, while supplying the processing gas toward the substrate independently from a central and a peripheral portion of a gas supply unit, which face the central and the periphery part of the substrate respectively, the processing gas is supplied such that a gas flow rate is greater in the central portion than in the peripheral portion. When the substrate is etched by using a processing gas including a second gas containing halogen and carbon and having a carbon number of three or more per molecule, the processing gas is supplied such that a gas flow rate is greater in the peripheral portion than in the central portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of each of the followingapplications and describes the relationship of the earlier applications.The present application is a Continuation application of and claims thebenefit of priority from co-pending U.S. application Ser. No.13/415,566, filed Mar. 8, 2012, which is a Continuation application ofU.S. application Ser. No. 12/690,802, filed on Jan. 20, 2010, which is aDivisional application of U.S. application Ser. No. 11/389,041, which isnow U.S. Pat. No. 7,674,393, patented on Mar. 9, 2010, which claims thebenefit of priority from U.S. Provisional Application No. 60/666,574,filed on Mar. 31, 2005 and is further based upon and claims the benefitof priority from the prior Japanese Patent Application No. 2005-087889,filed on Mar. 25, 2005. The entire contents of foregoing applicationsare incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a technology for performing an etchingon an etching target film formed on a substrate such as a semiconductorwafer by using a gas containing carbon and halogen.

BACKGROUND OF THE INVENTION

In a manufacturing process of a semiconductor device or an LCDsubstrate, an etching process is performed to form a pattern of a thinfilm. As one of a variety of etching apparatuses, for example, there isa parallel plate plasma etching apparatus, wherein parallel plateelectrodes including a pair of an upper and a lower electrode aredisposed in a chamber, and a high frequency electric field is formedtherebetween by applying a high frequency power to either one of theelectrodes while introducing a processing gas into the chamber. Due tothe high frequency electric field, a plasma of the processing gas isgenerated, whereby an etching process is performed on, e.g., asemiconductor wafer (hereinafter, referred to as a “wafer”) W.

For example, in the semiconductor device, a low dielectric film (low-kfilm) is practically used or tested as an interlayer insulating film, agate insulating film or the like. As the low dielectric film includingsilicon (Si) and oxygen (O), for example, there are an SiOC film formedby adding carbon to an SiO film serving as a base film and an SiOCH filmformed by adding carbon and hydrogen onto the SiO film. When etchingthose films, a gas containing carbon (C) and halogen such as fluorine(F), chlorine (Cl) and bromine (Br) is used as a processing gas.

In etching, a hole (recess) is formed by an etching action of an etchanttogether with polymerization which forms polymer on a sidewall of thehole to protect the sidewall. For example, when the SiO-based film isetched by using a gas containing carbon and fluorine (hereinafter,referred to as a “CF-based gas”) as a processing gas, active species ofCF, which are produced when the CF-based gas is converted into a plasma,cause both the etching and the polymerization.

The CF-based gases such as CF₄ gas, CHF₃ gas, C₂F₆ gas, C₃F₈ gas, C₄F₈gas, C₄F₆ gas, and C₅F₈ gas have different etching action andpolymerization. Therefore, although etching target films are the same,the most suitable kind of gas is selected from the CF-based gasesdepending on a film thickness ratio of the etching target film to anunderlying film or a resist film.

Further, in the conventional parallel plate plasma etching apparatus, inorder to improve uniformity of etching characteristics (e.g., an etchingrate and processing dimensions after etching) on the surface of thewafer W, the processing gas is supplied toward the wafer W from theupper electrode configured as a shower head having a plurality of gasinjection openings, for instance, while varying gas flow rates suppliedonto a center part and a periphery part of the wafer W.

However, due to lack of a consistent and reliable method for determininga flow rate ratio of gases supplied to the central and the peripherypart for respective CF-based gases, the flow rate ratio is determinedthrough many trials and errors to perform an etching process with a highin-surface uniformity. Thus, a lot of efforts and time are necessary todetermine the flow rate ratio.

Japanese Patent Laid-open Application No. 2002-184764 discloses atechnology wherein when an etching process is performed on TEOS and aresist by using a gaseous mixture including C₅F₈ gas, gaseous mixtureshaving different flow rate ratios are supplied from two gas injectionopenings of the shower head which are concentrically formed such that anoxygen flow rate is lower in the periphery part, thereby preventing anetching selectivity (TEOS/resist) in the periphery part from beingdeteriorated. Even in the aforementioned patent document, however, thereis not disclosed a consistent and reliable method for determining a flowrate ratio of gases supplied to the central and the periphery part ofthe wafer W when an etching is performed by using the CF-based gas.

SUMMARY OF THE INVENTION

The present invention has been conceived from the above problems; and itis, therefore, an object of the present invention to provide atechnology capable of improving in-surface uniformity when an etching isperformed on a substrate by using gas containing carbon and halogen.

In accordance with one embodiment of the present invention, there isprovided an etching method of performing etching on an etching targetfilm of a substrate by using a processing gas including a first gascontaining halogen and carbon and having a carbon number of two or lessper molecule, and a gas supply unit for supplying the processing gastoward the substrate from a central portion and a peripheral portion ofthe gas supply unit, independently, the central and the peripheralportion respectively facing the central and the periphery part of thesubstrate, the method including the step of performing etching on theetching target film of the substrate while supplying the processing gasfrom the gas supply unit such that a flow rate of the first gas per unitarea of a gas supply surface of the gas supply unit is greater in thecentral portion than in the peripheral portion.

Further, in accordance with another embodiment of the present invention,there is provided an etching method of performing etching on an etchingtarget film of a substrate by using a processing gas including a secondgas containing halogen and carbon and having a carbon number of three ormore per molecule, and a gas supply unit for supplying the processinggas toward the substrate from a central portion and a peripheral portionof the gas supply unit, independently, the central and the peripheralportion respectively facing the central and the periphery part of thesubstrate, the method including the step of performing etching on theetching target film of the substrate while supplying the processing gasfrom the gas supply unit such that a flow rate of the second gas perunit area of a gas supply surface of the gas supply unit is greater inthe peripheral portion than in the central portion.

Further, in accordance with still another embodiment of the presentinvention, there is provided an etching method of performing etching onan etching target film of a substrate by using a processing gas which isa gaseous mixture including a first gas containing halogen and carbonand having a carbon number of two or less per molecule and a second gascontaining halogen and carbon and having a carbon number of three ormore per molecule, and a gas supply unit for supplying the processinggas toward the substrate from a central portion and a peripheral portionof the gas supply unit, independently, the central and the peripheralportion respectively facing the central and the periphery part of thesubstrate, the method including the step of performing etching on theetching target film of the substrate while supplying the processing gasfrom the gas supply unit, wherein a mixing ratio of the first gas to thesecond gas in the central portion is equal to that in the peripheralportion; and if a total number of halogen atoms supplied along with thefirst gas is greater than that of halogen atoms supplied along with thesecond gas, the processing gas is supplied such that a flow rate of thegaseous mixture per unit area of a gas supply surface of the gas supplyunit is greater in the central portion than in the peripheral portion,and if the total number of halogen atoms supplied along with the firstgas is smaller than that of halogen atoms supplied along with the secondgas, the processing gas is supplied such that a flow rate of the gaseousmixture per unit area of a gas supply surface of the gas supply unit isgreater in the peripheral portion than in the central portion. In theetching method, the step of supplying the processing gas from the gassupply unit such that a supply amount of the gaseous mixture includingthe first gas and the second gas is greater or smaller in the centralportion than in the peripheral portion is performed by controlling atleast one of a flow rate of the processing gas and a dilution rate ofthe processing gas diluted with the dilution gas.

Further, in accordance with still another embodiment of the presentinvention, there is provided an etching method of performing etching onan etching target film of a substrate by using a processing gas which isa gaseous mixture including a first gas containing halogen and carbonand having a carbon number of two or less per molecule and a second gascontaining halogen and carbon and having a carbon number of three ormore per molecule, and a gas supply unit for supplying the processinggas toward the substrate from a central portion and a peripheral portionof the gas supply unit, independently, the central and the peripheralportion respectively facing the central and the periphery part of thesubstrate, the method including the step of performing etching on theetching target film of the substrate while supplying the processing gasfrom the gas supply unit, wherein a first processing gas produced bymixing the first gas with the second gas at a first mixing ratio issupplied to the central portion of the gas supply unit, and a secondprocessing gas produced by mixing the first gas with the second gas at asecond mixing ratio is supplied to the peripheral portion of the gassupply unit; and if a total number of halogen atoms supplied along withthe first gas is greater than that of halogen atoms supplied along withthe second gas, the processing gas is supplied such that a flow rate ofthe first processing gas is greater than that of the second processinggas per unit area of the gas supply surface of the gas supply unit, andif the total number of halogen atoms supplied along with the first gasis smaller than that of halogen atoms supplied along with the secondgas, the processing gas is supplied such that a flow rate of the firstprocessing gas is smaller than that of the second processing gas perunit area of the gas supply surface of the gas supply unit.

Further, in accordance with still another embodiment of the presentinvention, there is provided an etching method of performing etching onan etching target film of a substrate by using a processing gas which isa gaseous mixture including a first gas containing halogen and carbonand having a carbon number of two or less per molecule and a second gascontaining halogen and carbon and having a carbon number of three ormore per molecule, and a gas supply unit for supplying the processinggas toward the substrate from a central portion and a peripheral portionof the gas supply unit, independently, the central and the peripheralportion respectively facing the central and the periphery part of thesubstrate, the method including the step of performing etching on theetching target film of the substrate while supplying the processing gasfrom the gas supply unit such that a flow rate of the first gas per unitarea of the gas supply surface of the gas supply unit is greater in thecentral portion than in the peripheral portion and a flow rate of thesecond gas per unit area of the gas supply surface of the gas supplyunit is greater in the peripheral portion than in the central portion.

Further, in accordance with still another embodiment of the presentinvention, there is provided an etching method of performing etching onan etching target film of a substrate by using a processing gas which isa gaseous mixture including a first gas containing halogen and carbonand having a carbon number of two or less per molecule and a second gascontaining halogen and carbon and having a carbon number of three ormore per molecule, and a gas supply unit for supplying the processinggas toward the substrate from a central portion and a peripheral portionof the gas supply unit, independently, the central and the peripheralportion respectively facing the central and the periphery part of thesubstrate, the method including the step of performing etching on theetching target film of the substrate while supplying the processing gasfrom the gas supply unit wherein if a supply amount of the first gas inthe central portion of the gas supply unit is equal to that in theperipheral portion thereof, the processing gas is supplied such that aflow rate of the second gas per unit area of the gas supply surface ofthe gas supply unit is greater in the peripheral portion than in thecentral portion, and if a supply amount of the second gas in the centralportion of the gas supply unit is equal to that in the peripheralportion thereof, the processing gas is supplied such that a flow rate ofthe first gas per unit area of the gas supply surface of the gas supplyunit is greater in the central portion than in the peripheral portion.

In the etching method, the step of supplying the processing gas from thegas supply unit such that a supply amount of the first gas is greater inthe central portion than in the peripheral portion is performed bycontrolling at least one of a flow rate of the first gas and a dilutionrate of the first gas diluted with the dilution gas. Further, the stepof supplying the processing gas from the gas supply unit such that asupply amount of the second gas is greater in the peripheral portionthan in the central portion is performed by controlling at least one ofa flow rate of the second gas and a dilution rate of the second gasdiluted with the dilution gas.

Further, in accordance with still another embodiment of the presentinvention, there is provided an etching method of performing etching onan etching target film of a substrate by using a processing gas which isa gaseous mixture including a first gas containing halogen and carbonand having a carbon number of two or less per molecule and a second gascontaining halogen and carbon and having a carbon number of three ormore per molecule, and a gas supply unit for supplying the processinggas toward the substrate from a central portion and a peripheral portionof the gas supply unit, independently, the central and the peripheralportion respectively facing the central and the periphery part of thesubstrate, the method including the step of setting a composition and anamount of the processing gas supplied from the gas supply unit, whereinif a total number of halogen atoms supplied along with the first gas isgreater than that of halogen atoms supplied along with the second gas,the processing gas is set such that a total number of halogen atoms perunit area of the gas supply surface of the gas supply unit per unit timeis greater in the central portion than in the peripheral portion, and ifthe total number of halogen atoms supplied along with the first gas issmaller than that of halogen atoms supplied along with the second gas,the processing gas is supplied such that the total number of halogenatoms per unit area of the gas supply surface of the gas supply unit perunit time is greater in the peripheral portion than in the centralportion.

In the etching method, at least one of CH₂F₂ gas, CHF₃ gas, CF₄ gas andC₂F₆ gas may be used as the first gas, and at least one of C₃F₈ gas,C₄F₈ gas, C₄F₆ gas and C₅F₈ gas may be used as the second gas.

Such an etching method is performed by an etching apparatus, including aprocessing chamber in which a susceptor for mounting a substrate thereonis disposed; a gas supply unit, disposed in the processing chamber toface the susceptor and having a surface facing the susceptor serving asa gas supply surface, for supplying a processing gas containing carbonand halogen toward the substrate mounted on the susceptor from a centralportion and a peripheral portion of the gas supply unit, independently,the central and the peripheral portion respectively facing the centraland the periphery part of the substrate; a means for controlling apressure inside the processing chamber; a means for generating a plasmain the processing chamber; a means for controlling a flow rate of theprocessing gas supplied to the gas supply unit; and a controller forcontrolling each of the means, wherein an etching target film formed onthe substrate is etched by a plasma of the processing gas.

As described above, in accordance with the present invention, whenetching is performed on an etching target film formed on a substrate byusing a processing gas including a gas containing carbon and halogen, asupply amount of the gas containing carbon and halogen is controlled,according to the carbon number of the gas containing carbon and halogen,in such a manner that a greater flow rate is supplied to the centralportion of the gas supply surface than to the peripheral portion andvice versa. Therefore, high in-surface uniformity of etchingcharacteristics such as an etching rate, processing accuracy afteretching can be achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of preferred embodimentsgiven in conjunction with the accompanying drawings, in which:

FIG. 1 is a vertical sectional view showing a plasma etching apparatusin accordance with a preferred embodiment of the present invention;

FIG. 2 shows a configuration of a gas supply system of the plasmaetching apparatus;

FIG. 3 shows a configuration of another example of a gas supply systemof the plasma etching apparatus;

FIG. 4 offers a characteristic graph showing simulation results forin-surface uniformity of a gas flow speed;

FIG. 5 presents a characteristic graph showing simulation results forin-surface uniformity of a pressure;

FIG. 6 depicts a characteristic graph showing in-surface uniformity of afilm formation speed;

FIGS. 7A and 7B are, respectively, characteristic graphs showingin-surface uniformity of CF density and CF₂ density in Embodiment 1;

FIGS. 8A and 8B show in-surface uniformity of a residual resist film, anetching depth, a top CD and a bowing position in Embodiment 2;

FIGS. 9A and 9B are characteristic graphs showing in-surface uniformityof absolute values of a top CD difference and a etching depth,respectively, in Embodiment 3;

FIG. 10 shows in-surface uniformity of a residual resist film, a top CD,a bottom CD and a recess in Embodiment 4;

FIGS. 11A and 11B present in-surface uniformity of a taper angle θ inEmbodiment 5;

FIG. 12 is a characteristic graph showing in-surface uniformity of anabsolute value of a top CD difference in Embodiment 6;

FIG. 13 shows in-surface uniformity of a top CD and a bottom CD inEmbodiment 7;

FIGS. 14A and 14B depict characteristic graphs showing in-surfaceuniformity of a CD shift value in Embodiment 8;

FIG. 15 shows in-surface uniformity of an etching rate, a resistselectivity, a residual resist film and an etching depth in Embodiment9;

FIG. 16 offers a characteristic graph showing in-surface uniformity of aCD shift value in Embodiment 10;

FIG. 17 is a characteristic graph showing in-surface uniformity of a CDin Embodiment 11; and

FIG. 18 displays in-surface uniformity of an etching rate in Embodiment12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Above all, there will be briefly described an example of a plasmaetching apparatus for performing an etching method in accordance with afirst preferred embodiment of the present invention with reference toFIG. 1. FIG. 1 shows a chamber 1 which is, for example, a cylindricalprocessing vessel formed of, e.g., aluminum whose surface is alumitetreated (anodic oxidized); and the chamber 1 is grounded. Provided in abottom portion of the chamber 1 is an approximately cylindricalsusceptor 2 for mounting thereon a substrate such as a semiconductorwafer (hereinafter, referred to as a “wafer”). Further, the susceptor 2also serves as a lower electrode and is connected to a high pass filter(HPF) 23. Reference numerals 21 and 22 in FIG. 1 refer to an insulatingplate made of ceramic or the like and a susceptor support member,respectively. A reference numeral 24 in FIG. 1 refer to a coolantchamber to which a coolant such as liquid nitrogen is supplied to becirculated therein, so that the susceptor 2 can be maintained at adesired temperature by heat conduction.

The susceptor 2 has an upper central portion of disk shape, whichprotrudes higher than its peripheral portion, and an electrostatic chuck3 that is shaped substantially identical to the wafer W is disposed onthe upper central portion of the susceptor 2. Further, the electrostaticchuck 3 includes an electrode 31 therein. The wafer W iselectrostatically adsorbed onto electrostatic chuck 3 by Coulomb forcegenerated by a DC voltage of, for example, 1.5 kV applied to theelectrode 31 from a DC power supply 32. A reference numeral 33 in FIG. 1refer to a gas channel for supplying a heat transfer medium, e.g., a Hegas, to a backside surface of the wafer W supported on the susceptor 2,wherein heat is transferred between the susceptor 2 and the wafer Wthrough the heat transfer medium, so that the wafer W can be maintainedat a predetermined temperature. A reference numeral 25 in FIG. 1 referto an annular focus ring disposed to surround the wafer W loaded on theelectrostatic chuck 3. The focus ring 25 is formed of an electricallyconductive material such as silicon and functions to improve uniformityof etching.

A gas supply unit 4 also serving as an upper electrode of, e.g., anapproximately cylindrical shape is disposed above the susceptor 2 toface it in parallel. The gas supply unit 4 includes an electrode plate42 forming a facing surface to the susceptor 2 and having a plurality ofinjection openings 41; and an electrode support member 43 for supportingthe electrode plate 42. Further, the electrode support member 43 has awater cooling structure and is formed of, for example, aluminum whosesurface is alumite treated.

The electrode support member 43 includes a gas introduction chamberformed therein, which is divided into two inner and outer parts whichare, respectively, a first gas chamber (first gas introduction chamber)45 facing a center part of the wafer W and a second gas chamber (secondgas introduction chamber) 46 facing a periphery part of the wafer W by apartition wall 44 of, e.g., a ring shape. Thus, bottom surfaces of thefirst gas chamber 45 and the second gas chamber 46 are formed with theelectrode plate 42 having the injection openings 41 and serving as a gassupply surface.

Further, for instance, as shown in FIG. 2, the first gas chamber 45 isconnected to a processing gas supply system 53 via a first gasintroduction line 51 provided with a flow rate control unit F1; and thesecond gas chamber 46 is connected to the processing gas supply system53 via a second gas introduction line 52 provided with a flow ratecontrol unit F2. A reference numeral 47 in FIG. 1 refer to an insulationmember; reference numeral 48, a high frequency absorbing member; andreference numeral 49, an insulation member for supporting the gas supplyunit 4 in the chamber 1. Further, the susceptor 2 and the gas supplyunit 4 are spaced from each other by, for example, about 10˜60 mm.

A low dielectric film (low-k film) described above such as an SiOC film,an SiOCH film, an SiO₂ film, an SiOF film, an SiO₂ film containing Si—H,a HydrogenSilses-Quioxane (HSQ) film, a porous silica film, a SiO₂ filmcontaining a methyl group, a MethylSilses-Quioxane (MSQ) film, a porousMSQ film or the like can be used as an etching object film. As for theprocessing gas, a gas containing carbon and a halogen atom such asfluorine, bromine and chlorine is used as a main etching gas. Asexamples of a CF-based gas containing carbon and fluorine employed as amain etching gas, there are a first gas having a carbon number of 2 orless (e.g., CF₄ gas, CHF₃ gas, and C₂H₆ gas), and a second gas having acarbon number of 3 or more (e.g., C₃F₈ gas, C₄F₆ gas, C₄F₈ gas, and C₅F₈gas). Moreover, as the processing gas, it is possible to use a gaseousmixture obtained by mixing the CF-based gas with a rare gas or adilution gas such as, N₂ gas, H₂ gas, O₂ gas, CO gas and CO₂ gas withoutcontaining halogen atom, or a combination of a plurality of the CF-basedgases.

The processing gas supply system 53, for example, includes a first gassupply source 54 for supplying the first gas, a second gas supply source55 for supplying the second gas and a dilution gas supply source 56 forsupplying the dilution gas, which are connected to the first gasintroduction line 51 and the second gas introduction line 52 via asupply line 57 equipped with respective flow rate control units F3 toF5. The flow rate control units F1 to F5 for regulating a supply amountof the processing gas include a valve and a mass flow controller, andtheir operations are controlled by a controller 6. Thus, the first gas,the second gas and the dilution gas are mixed to make the processinggas, and the mixed processing gas is supplied to the first gasintroduction chamber 45 and the second gas introduction chamber 46 atspecified flow rates, respectively.

A vacuum pump 12 such as a turbo molecular pump for controlling thepressure in the chamber 1 is connected to a bottom portion of thechamber 1 via a gas exhaust pipe 11. Thus, the inside of the chamber 1can be evacuated to form therein a depressurized atmosphere having,e.g., a predetermined pressure of 1 Pa or less. Further, a gate valve 13is installed on a sidewall of the chamber 1. The wafer W is transferredbetween the chamber 1 and an adjacent load-lock chamber (not shown)while the gate valve 13 is opened.

The gas supply unit 4 serving as the upper electrode is connected to afirst high frequency power supply 61 serving as a plasma generationmeans through a matching unit 62 and a power feed rod 63, and, further,coupled to a low pass filter (LPF) 64. The first high frequency powersupply 61 has a frequency of 27 MHz or more. By applying a highfrequency power in such a range, a high-density plasma in a desirabledissociation state can be generated in the chamber 1, which makes itpossible to perform a plasma processing under a low pressure. In thisexample, the frequency of the first high frequency power supply 61 ischosen to be 60 MHz.

The susceptor 2 serving as the lower electrode is connected to a secondhigh frequency power supply 65 through a matching unit 66 installed in afeeder line. The second high frequency power supply 65 has a frequencyranging from 100 kHz to 10 MHz. By applying a power of a frequency insuch a range, a proper ionic action can be facilitated without causingany damage on the wafer W. In this example, the frequency of the firsthigh frequency power supply 65 is chosen to be 2 MHz.

Hereinafter, there will be described an etching method performed byusing the plasma etching apparatus in accordance with the presentinvention. First, in the plasma etching apparatus, after the gate valve13 is opened, the wafer W, i.e., a substrate, is loaded from theload-lock chamber (not shown) into the chamber 1 to be mounted on theelectrostatic chuck 3. Then, the wafer W is electrostatically adsorbedonto the electrostatic chuck 3 by applying a DC voltage from the highvoltage DC power supply 32 thereto. Next, the gate valve 13 is closed,and the inside of the chamber 1 is evacuated to a predetermined vacuumlevel by using the vacuum pump 12.

Subsequently, the processing gases from the processing gas supply system53 are introduced into the first gas chamber 45 and the second gaschamber 46 of the gas supply unit 4 through the first gas introductionline 51 and the second gas introduction line 52 while supply amounts arecontrolled by the flow rate control units F1, F2, respectively.Accordingly, the processing gas is supplied to the center part of thewafer W from the first gas chamber 45 while, at the same time, beingsupplied to the periphery part of the wafer W from the second gaschamber 46, and the pressure in the chamber 1 is maintained at apredetermined value.

Afterwards, a high frequency of 27 MHz or more, e.g., 60 MHz, is appliedto the gas supply unit 4 from the first high frequency power supply 61.Thus, high frequency electric field is generated between the gas supplyunit 4 and the susceptor 2, so that the processing gas is dissociated tobe converted into a plasma and the wafer W is etched by the plasma.

Meanwhile, a high frequency of 100 kHz˜10 MHz, for example, 2 MHz, isapplied to the susceptor 2 from the second high frequency power supply65. Accordingly, ions in the plasma are attracted into the susceptor 2,so that ion assist improves anisotropy of the etching. The wafer W onwhich the predetermined etching process has been performed as describedabove is transferred to the outside from the chamber 1, proceeding to anext step.

In the etching method of the present invention, when a SiO-based filmsuch as SiOC film is etched by a gas containing CF-based gas serving asthe main etching gas, a larger amount of the CF-based gas is supplied tothe center part of the wafer W than the periphery part and vice versadepending on the carbon number of the CF-based gas. Detailed descriptionthereof will be offered below.

First, there will be described a case where the CF-based gas and thedilution gas are mixed before being supplied to the plasma etchingapparatus. In such a case, the processing gases supplied to the firstgas chamber 45 and the second gas chamber 46 of the gas supply unit 4 inthe plasma etching apparatus have a same composition. Thus, flow ratesof the processing gases supplied to the first and the second gas chamber45 and 46 are controlled, whereby the amounts of the CF-based gasesincluded in the processing gases can be controlled to be supplied towardthe central and the periphery part.

Specifically, first, there will be described a case of using one kind ofthe CF-based gas. When the first gas whose carbon number is 2 or less isused as the main etching gas, the processing gases are introduced intothe gas supply unit 4 such that per unit area of the gas supply surfaceof the gas supply unit 4 per unit time, an amount of the first gassupplied to a central portion of the gas supply surface is greater thanthat supplied to a peripheral portion thereof.

That is, flow rates of the first gas and the dilution gas are controlledto be specified values by the flow rate control units F3 and F5 tothereby produce a processing gas wherein the first gas and the dilutiongas are mixed at a predetermined mixing ratio. Then, the processinggases are introduced into the first and the second gas chamber 45 and 46through the first and the second gas introduction line 51 and 52 atrespective flow rates by the flow rate control units F1 and F2 such thatthe amount of the processing gas supplied into the first gas chamber 45is greater than that supplied into the second gas chamber 46.Consequently, the central portion of the gas supply surface is suppliedwith a greater amount of the first gas than the peripheral portionthereof.

Here, “the supply amount of the first gas” used in the present inventionmeans a supply amount thereof per unit area of the gas supply surfaceper unit time. Further, “the central portion of the gas supply surfaceis supplied with a greater amount of the first gas than the peripheralportion thereof” means that the number of moles of the first gassupplied to the central portion is greater than that of the first gassupplied to the peripheral portion.

Further, when the second gas having the carbon number of 3 or more isused as the main etching gas, the processing gases are introduced intothe gas supply unit 4 such that per unit area of the gas supply surfaceof the gas supply unit 4 per unit time, an amount of the second gassupplied to the peripheral portion of the gas supply surface is greaterthan that supplied to the central portion thereof.

That is, flow rates of the second gas and the dilution gas arecontrolled to be specified values by the flow rate control units F4 andF5 to thereby produce a processing gas wherein the second gas and thedilution gas are mixed at a predetermined mixing ratio. Then, theprocessing gases are introduced into the first and the second gaschamber 45 and 46 through the first and the second gas introduction line51 and 52 at respective flow rates by the flow rate control units F1 andF2 such that the amount of the processing gas supplied into the secondgas chamber 46 is greater than that supplied into the first gas chamber45. Therefore, the peripheral portion of the gas supply surface issupplied with a greater amount of the first gas than the central portionthereof.

Here, “the central portion of the gas supply surface” means the gassupply surface of the first gas chamber 45, facing the center part ofthe wafer W occupying about seven-tenths (square root of a half) of itsradius. “The peripheral portion of the gas supply surface” means the gassupply surface of the second gas chamber 46, facing a periphery part ofthe wafer W surrounding the center part thereof. Further, areas of thecentral portion and the peripheral portion are designed to beapproximately equal to each other. In the plasma etching apparatus, thegas supply surface of the gas supply unit 4 faces the wafer W, and it isconfigured such that the processing gases are supplied from the firstand the second gas chamber 45 and 46 of the gas supply unit 4 toward thecentral and the periphery part of the wafer W, respectively. Therefore,when the amount of the first gas supplied to the central portion of thegas supply surface is set to be greater than that supplied to theperipheral portion thereof, the amount of the first gas supplied to thecenter part of the wafer W becomes greater than that supplied to theperiphery part thereof. On the other hand, when the amount of the secondgas supplied to the peripheral portion of the gas supply surface is setto be greater than that supplied to the central portion thereof, theamount of the second gas supplied to the periphery part of the wafer Wbecomes greater than that supplied to the center part thereof.

In this case, in the plasma etching apparatus, if the number of theinjection openings 41 formed on the bottom surface of the first chamber45 (injection openings for supplying a gas to the center part of thewafer W) is equal to that of the injection openings 41 formed on thebottom surface of the second chamber 46 (injection openings forsupplying a gas to the periphery part of the wafer W) and a gas flowrate ratio of the central portion to the peripheral portion of the gassupply surface is set at 5:5, a gas flow rate from each of the injectionopenings 41 is constant. However, if the number of the injectionopenings 41 formed on the bottom surface of the first chamber 45 isdifferent from that of the injection openings 41 formed on the bottomsurface of the second chamber 46 or if conductance to the injectionopenings 41 formed on the bottom surface of the first chamber 45 isdifferent from that to the injection openings 41 formed on the bottomsurface of the first chamber 46, adjustment therefor needs to be carriedout.

For example, a case where the ratio of the number of the injectionopenings 41 formed on the bottom surface of the first gas chamber 45versus that of the injection openings 41 formed on the bottom surface ofthe second gas chamber 46 is set to be 2:1, if the processing gases aresupplied to the center part and the periphery part at a flow rate ratioof 1:2, has a substantially same effect as the case where the processinggases are supplied to the center part and the periphery part at a flowrate ratio of 5:5 in the plasma etching apparatus. Therefore, when, forexample, C₄F₈ gas is used as the main processing gas, it is preferablethat two thirds of the entire processing gas or larger is supplied tothe periphery part.

Next, there will be described a case of using two or more kinds ofCF-based gas. For example, when the combination of the first gas and thesecond gas is used, the first gas, the second gas and the dilution gasare mixed at a predetermined mixing ratio by the flow rate control unitsF3 to F5 to produce the processing gas. The total number of halogenatoms introduced by each of the first and the second gas is calculated.The flow rates are determined depending on the kind of CF-based gashaving the greater total number. This is because the etching efficiencyis dominated by the number of halogen atoms, and thus the uniformity isdominated by a gas having a greater number of halogen atoms.

For example, in case that the first gas of CF₄ gas and the second gas ofC₄F₈ gas are mixed at a mixing ratio of 15:6 (CF₄:C₄F₈) to make theprocessing gas, the total number of F introduced by CF₄ gas is 4×15=60,and the total number of F introduced by C₄F₈ is 8×6=48. Namely, thetotal introduction number of F in the CF₄ is greater than C₄F₈. Thus,the flow rates are determined by the CF₄ gas. A greater amount of theprocessing gas is introduced to the first gas introduction chamber 45than to the second gas introduction chamber 46 by controlling the flowrate control units F1, F2 such that the amount of the processing gassupplied to the central portion of the gas supply surface is greaterthan that supplied to the peripheral portion thereof.

Similarly, in case that the total number of halogen atoms supplied alongwith the first gas is smaller than that supplied along with the secondgas, the amount of the processing gas introduced to the second gaschamber 46 is greater than that introduced to the first gas chamber 45by controlling the flow rate control units F1 and F2 such that theamount of the processing gas supplied to the peripheral portion of thegas supply surface is greater than that supplied to the central portionthereof.

Hereinafter, there will be described a second preferred embodiment ofthe present invention. In this embodiment, the compositions ofprocessing gases supplied to the central portion and the peripheralportion of the gas supply surface of the gas supply unit 4 arecontrolled independently, which is realized by, e.g., a plasma etchingapparatus shown in FIG. 3. In the plasma etching apparatus shownapparatus, for example, the first gas introduction line 51 provided withthe flow rate control unit F1 is connected to a first gas supply source161 for supplying the first gas, a second gas supply source 162 forsupplying the second gas and a dilution gas supply source 163 forsupplying the dilution gas via supply lines equipped with flow ratecontrol units F6, F7 and F8, respectively. Further, the second gasintroduction line 52 provided with the flow rate control unit F2 isconnected to a first gas supply source 164 for supplying the first gas,a second gas supply source 165 for supplying the second gas and adilution gas supply source 166 for supplying the dilution gas via asupply lines equipped with the flow rate control units F9, F10 and F11.

The flow rate control units F1, F2, F6 to F11 are controlled by thecontroller 6, and thus the processing gases having different mixingratios of the first gas, the second gas and the dilution gas (differentdilution rates) can be supplied to the first gas chamber 45 and thesecond gas chamber 46 through the first gas introduction line 51 and thesecond gas introduction line 52, respectively. And the otherconfiguration is same as the plasma etching apparatus shown in FIG. 1.

In this embodiment, in case that the processing gases have the samecomposition or that a CF-based gas is only supplied, the flow rates ofthe processing gases supplied to the first gas chamber 45 and the secondgas chamber 46 is controlled, thereby controlling the total number offluorine atoms (halogen atoms) supplied to the central portion of thegas supply surface and that supplied to the peripheral portion thereof.Besides, the processing gases having the different compositions can besupplied to the plasma etching apparatus. Accordingly, by varyingcompositions of the processing gases, that is, dilution rates of theCF-based gases, while flow rates of the processing gases supplied to thefirst gas chamber 45 and the second gas chamber 46 are kept to be equal,the total number of fluorine atoms (halogen atoms) supplied to thecentral portion of the gas supply surface and that supplied to theperipheral portion thereof may be controlled.

At this time, in case the first gas having the carbon number of 2 orless is used as the main etching gas, the amount of the first gassupplied to the first gas chamber 45 and that supplied to the second gaschamber 46 are controlled such that the total number of fluorine atomssupplied to the central portion of the gas supply surface is greaterthan that of fluorine atoms supplied to the peripheral portion thereof.

For example, in case that CF₄ gas is used as the first gas and thedilution gas is not used, the flow rate of CF₄ gas supplied to the firstgas chamber 45 is set at 100 sccm by the flow rate control units F1 andF6; and the flow rate of CF₄ gas supplied to the second gas chamber 46is set at 50 sccm by the flow rate control units F2 and F9. In otherwords, the gas flow rate supplied to the central portion of the gassupply surface is 100 sccm; and the gas flow rate supplied to theperipheral portion thereof is 50 sccm, so that the total number offluorine atoms supplied to central portion of the gas supply surface isgreater that supplied to the peripheral portion thereof. In this case, asingle flow rate control unit may be provided between the first gaschamber 45 and the first gas supply source 161 or between the first gaschamber 45 and the second gas supply source 162. Further, it is possibleto provide only one flow rate control unit between the second gaschamber 46 and the first gas supply source 164 or between the second gaschamber 46 and the second gas supply source 165.

Further, for example, in case that the first gas of CF₄ gas and thedilution gas of Ar gas are employed while varying the dilution rates ofthe first gases supplied to the central portion and the peripheralportion of the gas supply surface, the first gas having a flow rate of50 sccm and the dilution gas having a flow rate of 100 sccm are suppliedto first gas introduction line 51 via the flow rate control units F6 andF8 while, at the same time, the first gas having a flow rate of 50 sccmand the dilution gas having a flow rate of 300 sccm are supplied to thesecond gas introduction line 52 via the flow rate control units F9 andF11. Then, by controlling the flow rate control units F1 and F2,processing gases of the same flow rate are supplied to the first gaschamber 45 and the second gas chamber 46 from the first gas introductionline 51 and the second gas introduction line 52, respectively.

As described above, by supplying the processing gases at a same flowrate to the first gas chamber 45 and the second gas chamber 46; andmaking the dilution rate of the first gas diluted with the dilution gasgreater in the processing gas supplied to the second gas chamber 46 thanin the processing gas supplied to the first gas chamber 45, the totalnumber of fluorine atoms supplied to the central portion of the gassupply surface can be controlled to be greater than that of fluorineatoms supplied to the peripheral portion thereof.

Similarly, in case of using the second gas having the carbon number of 3or more as the main etching gas, amounts of the second gases supplied tothe central portion and the peripheral portion of the gas supply surfaceare controlled such that the total number of fluorine atoms in thesecond gas supplied to the central portion of the gas supply surface issmaller than that of the halogen atoms of the second gas supplied to theperipheral portion thereof.

In the same way as in the case of using the first gas, in case that theprocessing gases have the same composition or that a CF-based gas isonly supplied, the larger amount of the second gas is supplied to thesecond gas chamber 46 that the first gas chamber 45, so that it can becontrolled that the total number of fluorine atoms supplied to theperipheral portion of the gas supply surface is greater than that offluorine atoms supplied to the central portion thereof. Besides, byvarying compositions of the processing gases, that is, dilution rates ofthe second gases, while the amounts of the processing gases supplied tothe first gas chamber 45 and the second gas chamber 46 are kept to beequal, it can be controlled that the total number of fluorine atomssupplied to the peripheral portion of the gas supply surface is greaterthan that supplied to the central portion thereof may be controlled.

Further, in case the first gas having the carbon number of 2 or less andthe second gas having a carbon number of 3 or more are mixed, the totalnumber of halogen atoms introduced by each CF-based gas is calculated,and then it is determined whether more halogen atoms are supplied to thecentral portion or the peripheral portion of the gas supply surface bythe CF-based gas having a greater number of halogen atoms.

When the processing gases having different mixing ratios of the firstgas to the second gas are respectively supplied to the first gas chamber45 and the second gas chamber 46, for example, when a first processinggas having a first mixing ratio of the first gas to the second gas issupplied to the first gas chamber 45 and a second processing gas havinga second mixing ratio of the first gas to the second gas is supplied tothe second gas chamber 46, after calculating the total number of halogenatoms introduced by each CF-based gas in the entire processing gasincluding the first and the second processing gas, the amount of thefirst gas supplied to the first gas chamber 45 and the amount of thesecond gas supplied to the second gas chamber 46 are determined by theCF-based gas having a greater number of halogen atoms.

That is, in case the number of fluorine atoms introduced by the firstgas is greater than that introduced by the second gas, the flow rates ofthe first processing gas and the second processing gas are controlled bythe flow rate control units F1 and F2 such that the amount of the firstprocessing gas supplied to the first gas chamber 45 is greater than thatof the second processing gas supplied to the second gas chamber 46.

On the other hand, in case the number of fluorine atoms introduced bythe second gas is greater than that introduced by the first gas, theflow rates of the first processing gas and the second processing gas arecontrolled by the flow rate control units F1 and F2 such that the amountof the first processing gas supplied to the first gas chamber 45 issmaller than that of the second processing gas supplied to the secondgas chamber 46.

In this case, the mixing ratio of the first gas to the second gas in thefirst processing gas is controlled by the flow rate control units F6 andF7, while the mixing ratio of the first gas to the second gas in thesecond processing gas is controlled by the flow rate control units F9and F10. Then, the amounts of the first and the second processing gas tobe supplied to the first gas chamber 45 and the second gas chamber 46are controlled by the flow rate control units F1 and F2, respectively.

Further, in case the first gas having the carbon number of 2 or less andthe second gas having the carbon number of 3 or more are mixed, theamounts of the first gas and the second gas respectively supplied to thefirst gas chamber 45 and the second gas chamber 46 may be controlledsuch that a greater amount of the first gas is supplied to the centralportion than to the peripheral portion and that a greater amount of thesecond gas is supplied to the peripheral portion than to the centralportion.

Specifically, for example, in case CF₄ gas is used as the first gas andC₄F₈ is used as the second gas, C₄F₈ gas having a flow rate of 2 sccmand CF₄ gas having a flow rate of 10 sccm are supplied to the first gaschamber 45, while C₄F₈ having a flow rate of 4 sccm and CF₄ gas having aflow rate of 5 sccm are supplied to the second gas chamber 46. By doingso, the processing gas in the central portion of the gas supply surfacehas a greater amount of the first gas and a smaller mixing ratio of thesecond gas to the first gas than the processing gas in the peripheralportion. Further, the processing gas in the peripheral portion has agreater amount of the second gas and a greater mixing ratio of thesecond gas to the first gas than the processing gas in the centralportion. Therefore, the flow rate of the first gas is controlled in sucha manner that a greater amount of fluorine atoms is supplied to thecentral portion than to the peripheral portion of the gas supplysurface, while the flow rate of the second gas is controlled in such amanner that a greater amount of fluorine atoms is supplied to theperipheral portion than to the central portion.

In this case, the amount of the first gas supplied to the first gaschamber 45 is controlled by the flow rate control unit F1 or F6, whilethe amount of the first gas supplied to the second gas chamber 46 iscontrolled by the flow rate control unit F2 or F9. Further, the amountof the second gas supplied to the first gas chamber 45 is controlled bythe flow rate control unit F1 or F7, while the amount of the second gassupplied to the second gas chamber 46 is controlled by the flow ratecontrol unit F2 or F10. Accordingly, in this embodiment, only one flowrate control unit may be installed between the first gas chamber 45 andthe first gas supply source 161; between the first gas chamber 45 andthe second gas supply source 162; between the second gas chamber 46 andthe first gas supply source 164; or between the second gas chamber 46and the second gas supply source 165.

Further, in case the first gas having carbon number of two or less andthe second gas having a carbon number of three or more are mixed witheach other as described above, if the amount of the processing gassupplied to the first gas chamber 45 is equal to that supplied to thesecond gas chamber 46, the ratio of the first gas to the processing gasis set to be greater in the central portion than in the peripheralportion of the gas supply surface, while the ratio second gas to theprocessing gas is set to be greater in the peripheral portion than inthe central portion of the gas supply surface.

Further, in case the first gas having a carbon number of two or less andthe second gas having a carbon number of three or more are mixed witheach other, the flow rate of the first gas may be controlled such thatthe same amount of the first gas is supplied to the first gas chamber 45and the second gas chamber 46, whereas the flow rate of the second gasmay be controlled such that a greater amount of the second gas issupplied to the second gas chamber 46 than to the first gas chamber 45to thereby supply it to the peripheral portion than to the centralportion of the gas supply surface. For example, the first gas chamber 45is supplied with a gaseous mixture containing C₄F₈ gas having a flowrate of 2 sccm and CF₄ gas having a flow rate of 10 sccm, while thesecond gas chamber 46 is supplied with a gaseous mixture containing C₄F₈gas having a flow rate of 4 sccm and CF₄ gas having a flow rate of 10sccm.

At this time, by maintaining the flow rates of the processing gasessupplied to the first gas chamber 45 and the second gas chamber 46 to beequal, and at the same time, making the ratio of the first gas to theprocessing gas in the first gas chamber 45 equal to that in the secondgas chamber 46, it is possible to set the ratio of the second gas to theprocessing gas to be greater in the peripheral portion than in thecentral portion of the gas supply surface.

Further, the flow rate of the second gas may be controlled such that thesame amount of the second gas is supplied to the first gas chamber 45and the second gas chamber 46, whereas the flow rate of the first gasmay be controlled such that a greater amount of the first gas issupplied to the first gas chamber 45 than to the second gas chamber 46to thereby supply it to the central portion than to the peripheralportion of the gas supply surface. For example, the first gas chamber 45is supplied with a gaseous mixture containing C₄F₈ gas having a flowrate of 2 sccm and CF₄ gas having a flow rate of 10 sccm, while thesecond gas chamber 46 is supplied with a gaseous mixture containing C₄F₈gas having a flow rate of 2 sccm and CF₄ gas having a flow rate of 5sccm.

At this time, by maintaining the flow rates of the processing gasessupplied to the first gas chamber 45 and the second gas chamber 46 to beequal, and at the same time, making the ratio of the second gas to theprocessing gas in the first gas chamber 45 equal to that in the secondgas chamber 46, it is possible to set the ratio of the first gas to theprocessing gas to be greater in the central portion than in theperipheral portion of the gas supply surface.

By doing so, the processing gas in the central portion of the gas supplysurface has a smaller mixing ratio of the second gas to the first gasthan the processing gas in the peripheral portion. Further, theprocessing gas in the peripheral portion has a greater mixing ratio ofthe second gas to the first gas than the processing gas in the centralportion. Therefore, the flow rate of the first gas is controlled in sucha manner that a greater amount of fluorine atoms is supplied to thecentral portion than to the peripheral portion of the gas supplysurface, while the flow rate of the second gas is controlled in such amanner that a greater amount of fluorine atoms is supplied to theperipheral portion than to the central portion.

Also in this case, the amount of the first gas supplied to the first gaschamber 45 is controlled by the flow rate control unit F1 or F6, whilethe amount of the first gas supplied to the second gas chamber 46 iscontrolled by the flow rate control unit F2 or F9. Further, the amountof the second gas supplied to the first gas chamber 45 is controlled bythe flow rate control unit F1 or F7, while the amount of the second gassupplied to the second gas chamber 46 is controlled by the flow ratecontrol unit F2 or F10. Accordingly, a single flow rate control unit maybe installed between the first gas chamber 45 and the first gas supplysource 161; between the first gas chamber 45 and the second gas supplysource 162; between the second gas chamber 46 and the first gas supplysource 164; or between the second gas chamber 46 and the second gassupply source 165.

Further, in accordance with the present invention, in case the totalnumber of halogen atoms supplied along with the first gas is greaterthan that of supplied along with the second gas, the composition of theprocessing gas or the supply amount of the processing gas may becontrolled in such a manner that the total number of halogen atoms perunit area of the gas supply surface per unit time is greater in thecentral portion than in the peripheral portion. In such a case, thenumber of halogen atoms supplied along with the first gas and the secondgas is greater in the central portion than in the peripheral portion ofthe gas supply surface.

At this time, in case the total number of halogen atoms supplied alongwith the first gas is smaller than that supplied along with the secondgas, the composition of the processing gas or the supply amount of theprocessing gas may be set in such a manner that the total number ofhalogen atoms per unit area of the gas supply surface per unit time isgreater in the peripheral portion than in the central portion. In such acase, the number of halogen atoms supplied along with the first gas andthe second gas is greater in the peripheral portion than in the centralportion of the gas supply surface.

In the above-mentioned methods, according to the carbon number of theCF-based gas, the amount of CF-based gas supplied to the central portionis controlled to be greater or smaller than that supplied to theperipheral portion of the gas supply surface. Therefore, as will beclear in embodiments to be described later, it is possible to secure thein-surface uniformity of etching characteristics, such as an etchingrate or processing accuracy after etching, such as a top CD, a bottomCD, an etching residual film, an etching depth and a hole shape.

At this time, it has been determined in advance, depending on the carbonnumber in CF-based gas, which of the central portion and the peripheralportion of the gas supply surface is supplied with more halogen atoms.Therefore, it narrows down the scope of parameters used in determiningthe most appropriate condition for the flow rates and compositions ofthe processing gases supplied to the central portion and the peripheralportion of the gas supply surface and the like, readily setting thecondition.

EMBODIMENTS

Hereinafter, an evaluation method of the present invention will bedescribed. From various data obtained from the experiments, theinventors of the present invention found that a greater amount of thefirst gas having the carbon number of two or less is supplied to thecentral portion than to the peripheral portion of the gas supplysurface, and a greater amount of the second gas having the carbon numberof three or more is supplied to the peripheral portion than to thecentral portion of the gas supply surface in order to increase thein-surface uniformity of the etching characteristics such as the etchingrate or processing accuracy after etching.

First, a description will be offered on experiment examples conducted toprove the mechanism of the present invention.

FIG. 4 provides simulation results of gas flow speed distribution nearthe surface of the wafer W when the amounts of CF-based gases suppliedto the central portion and the peripheral portion of the gas supplysurface are changed by changing the flow rate ratio of the processinggas supplied to the first gas chamber 45 (the central portion of the gassupply surface) versus the processing gas supplied to the second gaschamber 46 (the peripheral portion of the gas supply surface) in theabove-described plasma etching apparatus, wherein it was assumed thatthe CF-based gas was C₄F₈. In FIG. 4, the vertical axis represents thegas flow speed and the horizontal axis represents the distance from thecenter of the wafer W. Further, a flow rate ratio C/E is a flow rate inthe central portion (C) to a flow rate in the peripheral portion (E) ofthe gas supply surface, wherein a dashed dotted line indicates a case ofC/E=3/7; a solid line, a case of C/E=5/5; and a dashed double-dottedline, a case of C/E=7/3. Further, the flow rate ratio C/E of 3/7 meansthat three-tenths of the flow rate of the entire processing gas issupplied to the central portion of the gas supply surface, whileseven-tenths of the flow rate of the entire processing gas is suppliedto the peripheral portion.

As a result, it is known that when a greater amount of the processinggas is supplied to the central portion than to the peripheral portion ofthe gas supply surface, the gas flow speed is the highest, and when agreater amount of the processing gas is supplied to the peripheralportion than to the central portion, the gas flow speed is the lowest.When a greater amount of the processing gas is supplied to the centralportion than to the peripheral portion, since the acceleration of thegas flow speed is greater compared to the case of supplying a greateramount of the processing gas to the peripheral portion, it is inferredthat the gas flows quickly from the center of the wafer W to the edgethereof.

On the other hand, when a greater amount of the processing gas issupplied to the peripheral portion than to the central portion, sincethe gas flow speed is low in the center part of the wafer W and becomeshigh suddenly in the periphery part thereof, it is inferred that the gasis stagnant in the center part, so that there are a large number ofmolecules whose residence time is long in the center part.

As for a CF-based gas whose molecule has a small carbon number of two orless, an etching action is strong due to a high ratio of F/C and thein-surface uniformity of etching rate is depended on the residence timeof the gas. Therefore, when a greater amount of the gas is supplied tothe peripheral portion, the residence time of the gas in the center partbecomes long, resulting in an excessive etching compared to theperiphery part, thereby deteriorating the in-surface uniformity.Contrarily, when a greater amount of the gas is supplied to the centralportion, since the gas flows quickly from the center to the edge of thewafer W, it is inferred that the residence time of the gas within thewafer W is more likely to be uniform, thus showing a high in-surfaceuniformity of the etching rate. Further, as for a CF-based gas whosemolecule has a large carbon number of three or more, polymerizationaction is high due to a low ratio of F/C, and it is inferred thatin-surface uniformity of the etching characteristics is more affected bydistribution of active species than by the residence time of the gas.

Therefore, as shown in FIG. 5, simulation was performed to obtainpressure distribution near the surface of the wafer W when the flow rateratio of the processing gas supplied to the central portion and theprocessing gas supplied to the peripheral portion of the gas supplysurface is changed, wherein it was assumed that the CF-based gas wasC₄F₈. In FIG. 5, the vertical axis represents the pressure, while thehorizontal axis represents the distance from the center of the wafer W.Further, a dashed double-dotted line indicates a case of C/E=3/7; asolid line, a case of C/E=5/5; and a dashed dotted line, a case ofC/E=7/3.

As a result, it was known that when a greater amount of the processinggas is supplied to the peripheral portion than to the central portion ofthe gas supply surface, the most uniform pressure distribution withinthe surface of the wafer W is achieved. The uniform pressuredistribution means that the density of molecules in the processing gasand the density of active species present within the surface of thewafer W become uniform. As described above, in case of the CF-based gashaving the carbon number of three or more, it is inferred that, when agreater amount of the processing gas is supplied to the peripheralportion than to the central portion, active species are more likely toexist uniformly throughout the surface of the wafer W, thus increasingthe in-surface uniformity of the etching.

Further, to support this, a film forming process was performed on a baresilicon by plasma of the processing gas under the following processingcondition in the plasma etching apparatus shown in FIG. 1 while varyingthe flow rates of the processing gases supplied to the central portionand the peripheral portion of the gas supply surface, wherein C₅F₈ wasused as CF-based gas, and Ar gas and O₂ gas are used as the dilutiongas. Then, the in-surface uniformity of the film forming speed wasmeasured.

<Processing Condition>

-   -   Flow rate ratio of C₅F₈ gas, Ar gas and O₂ gas;        -   C₅F₈:Ar:O₂=15:380:19 sccm    -   Processing pressure; 1.995 Pa (15 mTorr)    -   Processing temperature; 20° C.    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 2170 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 0 W

Results are shown in FIG. 6, wherein the vertical axis represents thefilm forming speed, while the horizontal axis represents the distancefrom the center of the wafer W. Further, □ indicates a case of the flowrate ratio C/E=7/3; 0 represents a case of C/E=5/5; and ▪ represents acase of C/E=3/7. From these results, it is proved that when the flowrate ratio C/E is 3/7, the film forming speed is the most uniformthroughout the surface of the wafer W. Therefore, it is confirmed thatwhen the flow rate supplied to the peripheral portion is greater thanthat supplied to the central portion, the pressure distribution becomesuniform, so that the density of active species becomes uniformthroughout the surface of the wafer W.

Hereinafter, respective embodiments will be described.

Embodiment 1

After the processing gas was produced in advance by mixing CHF₃ gasemployed as the CF-based gas; and Ar gas and N₂ gas employed as thedilution gas, an etching process was performed on a resist layer (formedon an entire surface of the wafer W without patterns formed thereon)formed on the wafer W under the following processing condition byintroducing the processing gas into the plasma etching apparatus shownin FIG. 1 while varying the amounts of the processing gases supplied tothe central portion and the peripheral portion of the gas supplysurface. Then, the in-surface uniformity of CF density and CF₂ densityon the wafer W was measured by utilizing an LIF (laser inducedfluorescence) technology. The flow rate ratios C/E of the processinggases were set to be 0/10, 3/7, 5/5, 7/3 and 10/0. Further, the flowrate ratio C/E of 0/10 means a case where the processing gas is suppliedonly to the peripheral portion of the gas supply surface.

<Processing Condition>

-   -   Flow rate ratio of CHF₃ gas, Ar gas and N₂ gas;        -   CHF₃:Ar:N₂=40:1000:80 sccm    -   Processing pressure; 6.65 Pa (50 mTorr)    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 1200 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 1700 W

FIG. 7A shows the in-surface uniformity of CF density, and FIG. 7Bpresents the in-surface uniformity of CF₂ density. In FIGS. 7A and 7B,the vertical axis represents CF density and CF₂ density, respectively,while the horizontal axis represents the distance from the center of thewafer W. Further, ▴ indicates a case of the flow rate ratio C/E=0/10; ▪indicates a case of C/E=7/3; 0 represents a case of C/E=5/5; □represents a case of C/E=3/7; and Δ represents a case of C/E=10/0.

From these results, it is known that both CF density and CF₂ density aremore uniform within the surface of the wafer W when the flow rate ishigher in the central portion of the gas supply surface than that in theperipheral portion. At this time, when the flow rate is higher in theperipheral portion, CF density is high in the center part of the waferW, while it is low in the periphery part of the wafer W. Thus, it isinferred that gas stagnation occurs in the center part of the wafer W asdescribed above. Contrarily, when the flow rate is higher in the centralportion, the density is low in the center part of the wafer W and isalmost uniform on the surface of the wafer W. Thus, it is inferred thatthe high in-surface uniformity of the gas flow speed distribution asdescribed above helps, for example, CF density become uniform within thesurface of the wafer W.

As described above, in case of the first gas having the carbon number oftwo or less, it is inferred that when the flow rate of the centralportion is higher, the amount of active species of CF or CF₂, activespecies of CF-based gas, becomes uniform within the surface of the waferW, so that the etching rate throughout the surface of the wafer Wbecomes uniform. Further, the inventors of the present inventionconducted a same experiment by using C₄F₈ gas as that conducted by usingCHF₃ gas, but since measurement values of LIF were small and lessreliable, the measurement data are not presented.

Embodiment 2

After the processing gas was produced in advance by mixing CHF₃ gasemployed as the CF-based gas; and Ar gas and N₂ gas employed as thedilution gas, an etching process was performed on an etching target film(SiOC film) formed on the wafer W under the following processingcondition by introducing the processing gas into the plasma etchingapparatus shown in FIG. 1 while varying the flow rates of the processinggases supplied to the central portion and the peripheral portion of thegas supply surface. Then, the in-surface uniformity of a residual resistfilm, an etching depth, a top CD and a bowing position was evaluated.Here, the flow rate ratios C/E of the processing gases supplied to thecentral portion and the peripheral portion of the gas supply surfacewere set to be 1/9, 5/5 and 9/1.

In FIG. 8A, a reference numeral 71 refers to the SiOC film serving asthe etching target film; and a reference numeral 72 refers to a resistfilm formed on the surface of the SiOC film. The residual resist film isrepresented by a distance A; the etching depth, a distance B; the bowingposition, a distance C from the top surface of the SiOC film to thegreatest diameter portion of a hole (recessed portion) 73 formed in theSiOC film; and the top CD, a top diameter D of the hole (recessedportion) 73 formed in the SiOC film.

Further, the distances A, B, C and the diameter D were measured in thecenter part and the periphery part of the wafer W by using across-sectional SEM (scanning electronic microscope) image of filmsafter etching, and in-surface uniformity thereof was evaluated in such amanner that the smaller a difference between values in the center partand the periphery part is, the better the in-surface uniformity gets.The center part of the wafer W means a rotational center of the wafer Wand the periphery part of the wafer W means a position 5 mm away fromthe outer periphery of the wafer W. The definitions of the residualresist film, the etching depth, the bowing position and the top CD, thedata measurement method and the method of evaluating the in-surfaceuniformity based on the difference between data values in the centerpart and the periphery part of the wafer W are the same also in thefollowing embodiments.

<Processing Condition>

-   -   Flow rate ratio of CHF₃ gas, Ar gas and N₂ gas;        -   CHF₃:Ar:N₂=40:1000:80 sccm    -   Processing pressure; 6.65 Pa (50 mTorr)    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 1200 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 1700 W

The results are tabled in FIG. 8B. In case of CHF₃ gas, for the residualresist film, the etching depth, the top CD, and the bowing position, thedifference (absolute value) between values in the center part and theperiphery part of the wafer W was smaller when a greater flow rate issupplied to the central portion than to the peripheral portion. Alsofrom this embodiment, it is understood that in case of CF-based gashaving the carbon number of two or less, when a greater flow rate issupplied to the central portion than to the peripheral portion, theetching rate becomes more uniform within the surface of the wafer W,thus improving the in-surface uniformity of the etching characteristicsof the residual resist film, the etching depth, the top CD, the bowingposition.

Embodiment 3

After the processing gas was produced in advance by mixing CHF₃ gasemployed as the CF-based gas; and Ar gas, N₂ gas and O₂ gas employed asthe dilution gas, an etching process was performed on an etching targetfilm (SiOCH film) formed on the wafer W under the following processingcondition by introducing the processing gas into the plasma etchingapparatus shown in FIG. 1 while varying the flow rates of the processinggases supplied to the central portion and the peripheral portion of thegas supply surface. Then, the in-surface uniformity of the top CD andthe etching depth formed by etching was evaluated.

<Processing Condition>

-   -   Processing pressure; 6.65 Pa (50 mTorr)    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 1500 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 2800 W

FIGS. 9A and 9B show the in-surface uniformity of the top CD and thein-surface uniformity of the etching depth, respectively. In FIG. 9A,the vertical axis represents an absolute value of difference of the topCD between the center part and the periphery part. In FIG. 9B, thevertical axis represents an absolute value of difference of the etchingdepth between the center part and the periphery part. Further, in FIGS.9A and 9B, the horizontal axis represents the flow rate ratio C/E ofgases supplied to the central portion and the peripheral portion. Forexample, the flow rate ratio 50% means that the flow rate ratio C/E is5/5, and the flow rate 90% means that the flow rate ratio C/E is 9/1.

From these results, it is proved that when the flow rate supplied to thecentral portion of the gas supply surface is greater, the difference ofthe top CD and the etching depth between the center part and theperiphery part of the wafer W is smaller, showing higher in-surfaceuniformity. Therefore, also from this embodiment, it is understood thatin case of the first gas having the carbon number of two or less, when agreater flow rate is supplied to the central portion than to theperipheral portion, the etching rate becomes more uniform within thesurface of the wafer W.

Embodiment 4

After the processing gas was produced in advance by mixing CH₂F₂ gasemployed as the CF-based gas; and O₂ gas employed as the dilution gas,an etching process was performed on an etching target film (laminatedfilm consisting of SiO film and SiOCH film) formed on the wafer W underthe following processing condition by introducing the processing gasinto the plasma etching apparatus shown in FIG. 1 while varying the flowrates of the processing gases supplied to the central portion and theperipheral portion of the gas supply surface. Then, the in-surfaceuniformity of the residual resist film, the top CD, the bottom CD andthe recess was evaluated. Here, the flow rate ratios C/E of theprocessing gases supplied to the central portion and the peripheralportion were set to be 1/9, 5/5 and 9/1.

<Processing Condition>

-   -   Flow rate ratio of CH₂F₂ gas, and O₂ gas;        -   CH₂F₂:O₂=40:20 sccm    -   Processing pressure; 7.98 Pa (60 mTorr)    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 700 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 300 W

The bottom CD is represented by a diameter E of a bottom portion of thehole 73 formed in the etching target film (SiOC film) 71 shown in FIG.8A, and the recess means an etching amount of an underlying film of theetching target film. Further, data on the evaluation items were measuredin the center part and the periphery part of the wafer W by using across-sectional SEM image of films after etching, and in-surfaceuniformity thereof was evaluated in such a manner that the smaller adifference between values in the center part and the periphery part is,the better the in-surface uniformity gets. The definitions of the bottomCD, the recess, the data measurement method and the method of evaluatingthe in-surface uniformity based on the difference between data values inthe center part and the periphery part of the wafer W are the same alsoin the following embodiments.

From results shown in FIG. 10, it is proved that when the flow rateratio C/E is 9/1, the difference of the top CD, the bottom CD and therecess between the center part and the periphery part of the wafer W issmaller, showing higher in-surface uniformity. Therefore, also from thisembodiment, it is understood that in case of the first gas having thecarbon number of two or less, when a greater flow rate is supplied tothe central portion than to the peripheral portion, the etching ratebecomes more uniform within the surface of the wafer W.

Embodiment 5

After the processing gas was produced in advance by mixing C₄F₈ gasemployed as the CF-based gas; and Ar gas and N₂ gas employed as thedilution gas, an etching process was performed on an etching target film(laminated film formed by laminating a tetraethyl orthosilicate (TEOS)film having the thickness of 50 nm and an bottom anti-reflection coating(BARC) having the thickness of 100 nm on a SiOC film) formed on thewafer W under the following processing condition by introducing theprocessing gas into the plasma etching apparatus shown in FIG. 1 whilevarying the flow rates of the processing gases supplied to the centralportion and the peripheral portion of the gas supply surface. Then, ashape of a hole formed by etching was evaluated. Here, the flow rateratios C/E of the processing gases supplied to the central portion andthe peripheral portion were set to be 1/9, 5/5 and 9/1.

<Processing Condition>

-   -   Flow rate ratio of C₄F₈ gas, Ar gas and N₂ gas;        -   C₄F₈:Ar:N₂=5:1000:150 sccm    -   Processing pressure; 6.65 Pa (50 mTorr)    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 500 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 2000 W

The hole shape was evaluated by measuring a taper angle θ formed betweenan outer surface 74 of a sidewall of the hole 73 and an extension line75 from a bottom surface of the hole, and calculating the difference ofthe taper angle θ of the hole between the center part and the peripherypart. The smaller difference means the better in-surface uniformity ofthe hole shape.

These results are shown in FIG. 11B. In FIG. 11B, the vertical axisrepresents the taper angle θ, while the horizontal axis represents theposition on the wafer W. Further, ⋄ indicates a case of the flow rateratio C/E=1/9; □, a case of C/E=5/5; and Δ, a case of C/E=9/1. From theresults, it is proved that when the flow rate ratio C/E is 1/9, thedifference of the taper angle θ between the center part and theperiphery part is the smallest, thus showing good in-surface uniformityof the hole shape. Therefore, it is understood that in case of thesecond gas having the carbon number of three or more, when a greaterflow rate is supplied to the peripheral portion than to the centralportion, the holes have more uniform shapes are within the surface ofthe wafer W.

Embodiment 6

After the processing gas was produced in advance by mixing C₄F₈ gas andCF₄ gas employed as the CF-based gas without the dilution gas, anetching process was performed on an etching target film (SiOCH film)formed on the wafer W under the following processing condition byintroducing the processing gas into the plasma etching apparatus shownin FIG. 1 while varying the flow rates of the processing gases suppliedto the central portion and the peripheral portion of the gas supplysurface. Then, the in-surface uniformity of the top CD was evaluated asdescribed above.

<Processing Condition>

-   -   Flow rate ratio of C₄F₈ gas and CF₄ gas;        -   C₄F₈:CF₄=5:200 sccm    -   Frequency of the first high frequency power supply 61; 60 MHz    -   Frequency of the second high frequency power supply 65; 2 MHz

Results are displayed in FIG. 12. In FIG. 12, the vertical axisrepresents an absolute value of difference of the top CD between thecenter part and the periphery part, while the horizontal axis representsthe flow rate ratio C/E of processing gases supplied to the centralportion and the peripheral portion. From these results, it is provedthat when the flow rate ratio C/E is 7/3, the top CD difference is thesmallest, showing high in-surface uniformity of the top CD.

In this embodiment, the flow rate ratio of C₄F₈ gas and CF₄ gas is 5:200sccm. Thus, the number of fluorine atoms supplied along with the CF₄ gasis greater than that of fluorine atoms supplied along with the C₄F₈ gas.In this case, it is understood that a greater flow rate is supplied tothe central portion of the gas supply surface than to the peripheralportion in accordance with the CF₄ gas to secure the in-surfaceuniformity of the top CD.

Embodiment 7

After a first etching process was performed by introducing theprocessing gas, which was produced in advance by mixing C₄F₈ gas and CF₄gas employed as the CF-based gas; and N₂ gas and O₂ gas employed as thedilution gas, into the chamber, a second etching process was performedby introducing the processing gas, which was produced in advance bymixing C₄F₈ gas employed as the CF-based gas; and Ar gas and N₂ gasemployed as the dilution gas, into the chamber. In this case, thein-surface uniformity of the top CD and the bottom CD was evaluated asdescribed above. Further, the etching process was performed on anetching target film (laminated film formed by laminating a TEOS filmhaving the thickness of 50 nm and an bottom anti-reflection coating(BARC) having the thickness of 65 nm on a SiOCH film) formed the wafer Wby using the plasma etching apparatus shown in FIG. 1 under thefollowing processing condition while changing the flow rates of theprocessing gas supplied to the central portion and the peripheralportion of the gas supply surface. The evaluation was conducted for acase of the flow rate ratio C/E=5/5 in both the first and the secondetching process, and a case of C/E=9/1 in the first etching process andC/E=1/9 in the second etching process.

<First Etching Processing Condition>

-   -   Flow rate ratio of C₄F₈ gas, CF₄ gas, N₂ gas and O₂ gas;        C₄F₈:CF₄:N₂:O₂=6:15:120:10 sccm    -   Processing pressure; 6.65 Pa (50 mTorr)    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 800 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 1400 W

<Second Etching Processing Condition>

-   -   Flow rate ratio of C₄F₈ gas, Ar gas and N₂ gas;        -   C₄F₈:Ar:N₂=8:50:1000 sccm    -   Processing pressure; 3.325 Pa (25 mTorr)    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 1000 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 3000 W

Results are shown in FIG. 13. From these results, it is proved that whena greater amount of the processing gas is supplied to the centralportion in the first etching process and to the peripheral portion inthe second etching process, the difference (absolute value) between dataof the top CD and the bottom CD in the center part and the peripherypart of the wafer W is smaller, showing higher in-surface uniformity ofthe CD.

Also in case that the first etching process and then the second etchingprocess were performed while changing kinds of the CF-based gas, asdescribed above, it is proved that the etching process can be performedwith the high in-surface uniformity by controlling the flow rates of theprocessing gases supplied to the central portion and the peripheralportion in accordance with the carbon number of each CF-based gas.

At this time, in the first etching process, the flow rate ratio of C₄F₈gas to CF₄ gas is C₄F₈:CF₄=6 sccm:15 sccm, and thus the number offluorine atoms supplied along with the CF₄ gas is greater than that ofthe fluorine atoms supplied along with the C₄F₈ gas. Therefore, it isunderstood that when a greater flow rate is supplied to the centralportion in accordance with the CF₄ gas, the top CD and the bottom CD aremore uniform within the surface of the wafer W. Further, in the secondetching process, since C₄F₈ gas is used, the top CD and the bottom CDare more uniform within the surface of the wafer W when a greater flowrate is supplied to the peripheral portion.

Embodiment 8

Etching processes were performed on an etching target film formed on thewafer W under the same etching condition as that in Embodiment 7, and anin-surface CD distribution was evaluated by CD-SEM (electron microscopewhich allows an inspection from the top surface of the wafer W withoutbreaking the wafer W). FIG. 14A shows results obtained in case of theflow rate ratio C/E=9/1 in the first etching process and C/E=1/9 in thesecond etching process. FIG. 14B shows results obtained in case of theflow rate ratio C/E=5/5 in both the first and the second etchingprocess. Further, in FIGS. 14A and 14B, the vertical axis represents aCD shift value; the horizontal axis, the position on the wafer; ⋄,X-axis data; and ◯, Y-axis data. The CD shift value in this embodimentmeans a difference of a diameter of a hole in a mask before and afteretching.

From these results, it is proved that when a greater flow rate issupplied to the central portion in the first etching process and agreater flow rate is supplied to the peripheral portion in the secondetching process, the CD shift values of the X-axis data and the Y-axisdata are small, showing the good uniformity of the in-surface CDdistribution.

Embodiment 9

After producing the processing gas in advance by mixing C₅F₈ gasemployed as the CF-based gas; and Ar gas and O₂ gas employed as thedilution gas, the etching process was performed by introducing theprocessing gas into the chamber. Then, uniformity of an etching rate,resist selectivity, a residual resist film and an etching depth wasevaluated. At this time, the etching process was performed on a resistformed on the wafer W under the following processing condition by usingthe plasma etching apparatus shown in FIG. 1, while varying the flowrates of the processing gas supplied to the central portion and theperipheral portion of the gas supply surface. The etching rate, theresist selectivity, the residual resist film and the etching depth wereevaluated for a case where a flow rate supplied to the central portionwas 208 sccm and a flow rate supplied to the peripheral portion was 208sccm, and a case where a flow rate supplied to the central portion was208 sccm and a flow rate supplied to the peripheral portion was 312sccm. Here, the etching selectivity is calculated by a ratio of anetching amount of SiO₂ film to a thickness reduction amount of a resistmask film. The values of the etching rate and the resist selectivity inthe center part and the periphery part of the wafer W were obtained byusing a cross-sectional SEM (scanning electronic microscope) image offilms after etching, and in-surface uniformity thereof was evaluated insuch a manner that the smaller a difference between the values in thecenter part and the periphery part is, the better the in-surfaceuniformity gets.

<Processing Condition>

-   -   Flow rate ratio of C₅F₈ gas, Ar gas, and O₂ gas;        -   C₅F₈:Ar:O₂=16:380:20 sccm    -   Processing pressure; 3.325 Pa (25 mTorr)    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 1000 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 3000 W

Results are shown in FIG. 15. From these results, it is proved that whena greater flow rate is supplied to the peripheral central portion thanto central portion of the gas supply surface, the difference of theetching rate, the etching selectivity and etching depth between thecenter part and the periphery part is small, showing high in-surfaceuniformity thereof.

Further, the flow rate supplied to the peripheral portion was changedwithout changing the flow rate supplied to the central portion in thisembodiment, and it is confirmed that although the flow rate supplied tothe peripheral portion is changed, if the flow rate supplied to thecentral portion is not changed, the etching characteristics in thecentral portion of the wafer W are not changed. Therefore, after settingthe total flow rate of the processing gas and the flow rates supplied tothe central portion and the peripheral portion, by increasing the flowrate supplied to the peripheral portion without any change in the flowrate supplied to the central portion, it is understood that the etchingcharacteristics in the periphery part can be changed while maintainingthe etching characteristics in the center part, thus improving thein-surface uniformity of the etching characteristics.

Embodiment 10

The etching process was performed by using the processing gas producedby mixing C₄F₈ gas employed as the CF-based gas; and CO gas, N₂ gas andO₂ gas employed as the dilution gas, and uniformity of the CD shiftvalue was evaluated. At this time, the etching process was performed onan etching target film (SiOC film) formed on the wafer W under thefollowing processing condition by using the plasma etching apparatusshown in FIG. 1, while varying the flow rates of the processing gassupplied to the central portion and the peripheral portion of the gassupply surface. The evaluation was made for cases where flow rate ratiosC/E were 2/4, 2/2, 2/6, respectively.

<Processing Condition>

-   -   Processing pressure; 6.65 Pa (50 mTorr)    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 800 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 1400 W

Results are shown in FIG. 16. From these results, it is proved that theCD shift value is greatly changed in the periphery part by changing theflow rate of C₄F₈ gas supplied the peripheral portion, and thein-surface uniformity of the CD shift is improved by supplying a greaterflow rate of C₄F₈ gas to the peripheral portion than to the centralportion.

Therefore, it is understood that the etching process can be performedwith high in-surface uniformity by changing a mixing ratio of the firstgas to the second gas in the processing gas supplied to the centralportion and the peripheral portion.

Embodiment 11

After a first etching process was performed by using the processing gasobtained by mixing CHF₃ gas and CF₄ gas employed as the CF-based gas;and Ar gas and N₂ gas employed as the dilution gas, a second etchingprocess was performed by using the processing gas obtained by mixingC₄F₈ gas employed as the CF-based gas; and Ar gas and N₂ gas employed asthe dilution gas. In this case, the in-surface uniformity of the top CDwas evaluated as described above. At this time, the etching process wasperformed on a resist formed on the wafer W by introducing theprocessing gas, which had been mixed at a predetermined ratio, into theplasma etching apparatus shown in FIG. 1 under the following processingconditions while changing the flow rates of the processing gasessupplied to the central portion and the peripheral portion.

<First Etching Processing Condition>

-   -   Flow rate ratio of CHF₃ gas, CF₄ gas, Ar gas and N₂ gas;        CHF₃:CF₄:Ar:N₂=15:15:500:80 sccm    -   Processing pressure; 6.65 Pa (50 mTorr)    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 800 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 1700 W

<Second Etching Processing Condition>

-   -   Flow rate ratio of C₄F₈ gas, Ar gas and N₂ gas;        -   C₄F₈:Ar:N₂=7:950:120 sccm    -   Processing pressure; 6.65 Pa (50 mTorr)    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 1200 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 1700 W

Further, the evaluation was conducted over a case where the flow rateratio C/E was 50/50 in both the first etching process and the secondetching process, and a case where the flow rate ratio C/E was 95/5 inthe first etching process and 5/95 in the second etching process.

Results are shown in FIG. 17. From these results, it is proved that whena greater flow rate of the processing gas is supplied to the centralportion in the first etching process and a greater flow rate of theprocessing gas is supplied to the peripheral portion in the secondetching process, the difference of the top CD between the center partand the periphery part is small, showing the good in-surface uniformityof the CD.

As described above, it is proved that when the first etching process wasperformed by using the processing gas produced by mixing CHF₃ gas, CF₄gas, Ar gas and N₂ gas, a greater flow rate of the processing gas issupplied to the central portion in accordance with the first gas havingthe carbon number of two or less, and the second etching process wasperformed by using the processing gas produced by mixing C₄F₈ gas, Argas and N₂ gas, a greater flow rate of the processing gas is supplied tothe peripheral portion in accordance with the second gas having thecarbon number of three or more, by supplying a greater amount of theprocessing gas to the peripheral portion, thus achieving the goodetching characteristics.

Embodiment 12

The etching process was performed by using the processing gas producedin advance by mixing C₄F₈ gas and CF₄ gas employed as the CF-based gas;and N₂ gas and O₂ gas employed as the dilution gas. Then, in-surfaceuniformity of an etching rate was evaluated. At this time, the etchingprocess was performed on a resist formed on the wafer W under thefollowing processing condition by using the plasma etching apparatusshown in FIG. 1, while varying the flow rates of the processing gassupplied to the central portion and the peripheral portion of the gassupply surface.

<Processing Condition>

-   -   Flow rate ratio of C₄F₈ gas, CF₄ gas, N₂ gas and O₂ gas;        C₄F₈:CF₄:N₂:O₂=6:15:120:10 sccm    -   Processing pressure; 6.65 Pa (50 mTorr)    -   Frequency and power of the first high frequency power supply 61;        60 MHz, 800 W    -   Frequency and power of the second high frequency power supply        65; 2 MHz, 1400 W

Further, the evaluation was conducted for a case of the flow rate ratioC/E=5/5, and a case of C/E=9/1.

Results are shown in FIG. 18. From these results, it is proved that whena greater flow rate of the processing gas is supplied to the centralportion, the difference of the etching rate between the center part andthe periphery part is small, showing the high in-surface uniformity ofthe etching rate.

Further, in case of supplying a gaseous mixture of the first gas and thesecond gas, it is proved that when the number of fluorine atoms suppliedalong with CF₄ gas is greater than that of fluorine atoms supplied alongwith C₄F₈, flow rates of the processing gases supplied the centralportion and the peripheral portion are controlled in accordance with theCF₄ gas to thereby obtain the good etching characteristics.

The present invention may be applied to a glass substrate employed in aflat display panel, such as an LCD and a PDP glass substrate, as well asthe semiconductor wafer W. Further, the plasma etching apparatus used inthe present invention may be of an RIE (reactive ion etching) type, anICP (inductive coupled plasma) type, an ECR (electron cyclotronresonance) type, a helicon wave plasma type or the like, all usingmagnetic field, instead of a parallel plate type plasma etchingapparatus.

While the invention has been shown and described with respect to thepreferred embodiments, it will be understood by those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. An etching apparatus for performing etching an etching target film ofa substrate by using a processing gas which is a gaseous mixtureincluding a first gas containing halogen and carbon and having a carbonnumber of two or less per molecule and a second gas containing halogenand carbon and having a carbon number of three or more per molecule, theetching apparatus comprising: a processing chamber in which a susceptorfor mounting the substrate thereon is disposed; a gas supply unit,disposed in the processing chamber to face the susceptor, for supplyingthe processing gas, the gas supply unit having a gas supply surfacefacing the susceptor; a first gas introduction line connected to acentral portion of the gas supply unit for supplying the processing gasto the central portion of the gas supply unit; a second gas introductionline connected to a peripheral portion of the gas supply unit forsupplying the processing gas to the peripheral portion of the gas supplyunit; a first flow rate control unit disposed at the first gasintroduction line; a second flow rate control unit disposed at thesecond gas introduction line; means for controlling a pressure insidethe processing chamber; means for generating a plasma in the processingchamber; and a controller for controlling the supply of the processinggas, wherein the gas supply unit comprises a first gas introductionchamber for supplying the processing gas to a central part of thesubstrate and a second gas introduction chamber for supplying theprocessing gas to a peripheral part of the substrate, wherein thecontroller is programmed to control a step of supplying the processinggas from the gas supply unit such that a flow rate of the first gas perunit area of the gas supply surface of the gas supply unit is greater inthe central portion than in the peripheral portion and a flow rate ofthe second gas per unit area of the gas supply surface of the gas supplyunit is greater in the peripheral portion than in the central portion.2. The etching apparatus of claim 1, wherein the processing gascomprises a dilution gas and at least one of a dilution rate of thefirst gas and that of the second gas is controlled by the dilution gas.3. The etching apparatus of claim 1, wherein the first gas is at leastone of CH₂F₂ gas, CHF₃ gas, CF₄ gas and C₂F₆ gas.
 4. The etchingapparatus of claim 1, wherein the second gas is at least one of C₃F₈gas, C₄F₈ gas, C₄F₆ gas and C₅F₈ gas.